// Sentence rules
// Intransitive:
// * Subject must be nominative case
// * Subject and verb must agree in number (copied through #1)
S -> N[ case: nom, num: #1 ] IV[ num: #1 ]
// Transitive:
// * Subject must be nominative case
// * Subject and verb must agree in number (copied through #2)
// * If there's a reflexive in the object position, make sure its `needs_pron`
// feature matches the subject's `pron` feature. If the object isn't a
// reflexive, then its `needs_pron` feature will implicitly be `**top**`, so
// will unify with anything.
S -> N[ case: nom, pron: #1, num: #2 ] TV[ num: #2 ] N[ case: acc, needs_pron: #1 ]
// Clausal:
// * Subject must be nominative case
// * Subject and verb must agree in number (copied through #1)
// * Reflexives can't cross clause boundaries (*"He said that she likes himself"),
// so we can ignore reflexives and delegate to inner clause rule
S -> N[ case: nom, num: #1 ] CV[ num: #1 ] Comp S
// Pronouns
// The added features are:
// * num: sg or pl, whether this noun wants a singular verb (likes) or
// a plural verb (like). note this is grammatical number, so for example
// singular they takes plural agreement ("they like X", not *"they likes X")
// * case: nom or acc, whether this noun is nominative or accusative case.
// nominative case goes in the subject, and accusative in the object.
// e.g., "he fell" and "she likes him", not *"him fell" and *"her likes he"
// * pron: he, she, they, or ref -- what type of pronoun this is
// * needs_pron: whether this is a reflexive that needs to bind to another
// pronoun.
N[ num: sg, case: nom, pron: he ] -> he
N[ num: sg, case: acc, pron: he ] -> him
N[ num: sg, case: acc, pron: ref, needs_pron: he ] -> himself
N[ num: sg, case: nom, pron: she ] -> she
N[ num: sg, case: acc, pron: she ] -> her
N[ num: sg, case: acc, pron: ref, needs_pron: she] -> herself
N[ num: pl, case: nom, pron: they ] -> they
N[ num: pl, case: acc, pron: they ] -> them
N[ num: pl, case: acc, pron: ref, needs_pron: they ] -> themselves
N[ num: sg, case: acc, pron: ref, needs_pron: they ] -> themself
// Names
// The added features are:
// * num: sg, as people are singular ("mary likes her" / *"mary like her")
// * case: **top**, as names can be both subjects and objects
// ("mary likes her" / "she likes mary")
// * pron: whichever pronoun the person uses for reflexive agreement
// mary pron: she => mary likes herself
// sue pron: they => sue likes themself
// takeshi pron: he => takeshi likes himself
N[ num: sg, case: **top**, pron: she ] -> mary
N[ num: sg, case: **top**, pron: they ] -> sue
N[ num: sg, case: **top**, pron: he ] -> takeshi
N[ num: sg, case: **top**, pron: he ] -> robert
// Complementizer doesn't need features
Comp -> that
// Verbs -- intransitive, transitive, and clausal
// The added features are:
// * num: sg, pl, or **top** -- to match the noun numbers.
// **top** will match either sg or pl, as past-tense verbs in English
// don't agree in number: "he fell" and "they fell" are both fine
// * tense: past or nonpast -- this won't be used for agreement, but will be
// copied into the final feature structure, and the client code could do
// something with it
IV[ num: sg, tense: nonpast ] -> falls
IV[ num: pl, tense: nonpast ] -> fall
IV[ num: **top**, tense: past ] -> fell
TV[ num: sg, tense: nonpast ] -> likes
TV[ num: pl, tense: nonpast ] -> like
TV[ num: **top**, tense: past ] -> liked
CV[ num: sg, tense: nonpast ] -> says
CV[ num: pl, tense: nonpast ] -> say
CV[ num: **top**, tense: past ] -> said